Question: If $x \oplus y = 2x-6$ and $x \boxdot y = x-4y$, find $(5 \boxdot -2) \oplus 4$.
Explanation: First, find $5 \boxdot -2$ $ 5 \boxdot -2 = 5-(4)(-2)$ $ \hphantom{5 \boxdot -2} = 13$ Now, find $13 \oplus 4$ $ 13 \oplus 4 = (2)(13)-6$ $ \hphantom{13 \oplus 4} = 20$.